ARGONAUT-III and -V: susceptibility of carbapenem-resistant Klebsiella pneumoniae and multidrug-resistant Pseudomonas aeruginosa to the bicyclic boronate β-lactamase inhibitor taniborbactam combined with cefepime

ABSTRACT Taniborbactam, a bicyclic boronate β-lactamase inhibitor with activity against Klebsiella pneumoniae carbapenemase (KPC), Verona integron–encoded metallo-β-lactamase (VIM), New Delhi metallo-β-lactamase (NDM), extended-spectrum beta-lactamases (ESBLs), OXA-48, and AmpC β-lactamases, is under clinical development in combination with cefepime. Susceptibility of 200 previously characterized carbapenem-resistant K. pneumoniae and 197 multidrug-resistant (MDR) Pseudomonas aeruginosa to cefepime-taniborbactam and comparators was determined by broth microdilution. For K. pneumoniae (192 KPC; 7 OXA-48-related), MIC90 values of β-lactam components for cefepime-taniborbactam, ceftazidime-avibactam, and meropenem-vaborbactam were 2, 2, and 1 mg/L, respectively. For cefepime-taniborbactam, 100% and 99.5% of isolates of K. pneumoniae were inhibited at ≤16 mg/L and ≤8 mg/L, respectively, while 98.0% and 95.5% of isolates were susceptible to ceftazidime-avibactam and meropenem-vaborbactam, respectively. For P. aeruginosa, MIC90 values of β-lactam components of cefepime-taniborbactam, ceftazidime-avibactam, ceftolozane-tazobactam, and meropenem-vaborbactam were 16, >8, >8, and >4 mg/L, respectively. Of 89 carbapenem-susceptible isolates, 100% were susceptible to ceftolozane-tazobactam, ceftazidime-avibactam, and cefepime-taniborbactam at ≤8 mg/L. Of 73 carbapenem-intermediate/resistant P. aeruginosa isolates without carbapenemases, 87.7% were susceptible to ceftolozane-tazobactam, 79.5% to ceftazidime-avibactam, and 95.9% and 83.6% to cefepime-taniborbactam at ≤16 mg/L and ≤8 mg/L, respectively. Cefepime-taniborbactam at ≤16 mg/L and ≤8 mg/L, respectively, was active against 73.3% and 46.7% of 15 VIM- and 60.0% and 35.0% of 20 KPC-producing P. aeruginosa isolates. Of all 108 carbapenem-intermediate/resistant P. aeruginosa isolates, cefepime-taniborbactam was active against 86.1% and 69.4% at ≤16 mg/L and ≤8 mg/L, respectively, compared to 59.3% for ceftolozane-tazobactam and 63.0% for ceftazidime-avibactam. Cefepime-taniborbactam had in vitro activity comparable to ceftazidime-avibactam and greater than meropenem-vaborbactam against carbapenem-resistant K. pneumoniae and carbapenem-intermediate/resistant MDR P. aeruginosa.

against WHO-priority pathogens such as carbapenem-resistant Gram-negative bacilli, 13 against Mycobacterium tuberculosis, and five against Clostridioides difficile.Twelve of these agents are β-lactam and β-lactamase inhibitor combinations, but it was noted that many are not active against metallo-β-lactamase (MBL) producers.The report also noted that, despite 11 new antibiotics being approved for use since 2017, these agents are from existing classes where resistance mechanisms are well established and have limited clinical benefit over existing treatment.Seven agents fulfilled at least one innovation criterion and two were active against multidrug-resistant (MDR) Gram-negative bacteria.Only two of the seven innovative antibiotics, taniborbactam (formerly VNRX-5133) in combination with cefepime and ledaborbactam (formerly VNRX-7145) in combination with ceftibuten, target at least one of the WHO critical priority antimicrobial-resistant Gram-negative bacterial groups.
β-Lactamase inhibitors have been an important component of antibacterials since the introduction of clavulanate into clinical use in 1984.Three classes of β-lactamase inhibitors are now in clinical use-agents with a β-lactam core (clavulanate, sulbac tam, and tazobactam), agents with a diazabicyclooctane (DBO) core (avibactam and relebactam), and agents with a boronic acid core (vaborbactam) (2).Vaborbactam inhibits Klebsiella pneumoniae carbapenemase (KPC) and other class A carbapenemases (IMI/NMC and SME), but not class D (OXA) or metallo (class B; IMP, NDM, VIM) types (3).Taniborbactam has been reported to have a broader spectrum of direct inhibition than any other β-lactamase inhibitor in use or in advanced clinical development, with cefepime-taniborbactam having similar coverage of carbapenem-resistant Enterobacter ales as β-lactam/DBO combinations, including aztreonam-avibactam, and cefiderocol (4,5).Taniborbactam is under clinical development in combination with cefepime at its highest approved dose (6 g/day in three divided doses) (6,7).In a phase 3, doubleblind, randomized trial, 661 hospitalized adults with complicated urinary tract infections, including acute pyelonephritis, were randomized in a 2:1 ratio to receive intravenous cefepime-taniborbactam (2.5 g) or meropenem (1 g) every 8 hours for 7 days (or up to 14 days for patients with concurrent bacteriemia) (6).Cefepime-taniborbactam was superior to meropenem regarding the primary composite outcome of both microbiologic and clinical success on trial days 19 to 23, with a treatment difference of 12.6% (95% CI, 3.1%-22.2%;P = 0.009).Higher composite success and clinical success rates were sustained at late follow-up (trial days 28 to 35).
This study was undertaken to evaluate the activity of cefepime-taniborbactam against collections of carbapenem-resistant K. pneumoniae and MDR Pseudomonas aeruginosa with characterized carbapenem resistance mechanisms, including those found in many regions of the United States (8-11).
Recent publications have documented the in vitro activity of cefepime-taniborbac tam.A study by Mushtaq et al. showed that cefepime-taniborbactam was active against Enterobacterales with KPC, other class A, OXA-48-like, VIM, and NDM carbapenemases, with MICs similar to those of ceftazidime-avibactam for Enterobacterales with KPC or OXA-48-like carbapenemases and a wider spectrum (3).Against the subset Entero bacterales with NDM (n = 124), cefepime-taniborbactam inhibited 89 (71.8%) isolates at ≤8 mg/L and 98 (79.0%) at ≤16 mg/L compared to <1% susceptible to ceftazidimeavibactam and meropenem-vaborbactam.The cefepime-taniborbactam MIC 90 value for  Enterobacterales with KPC in that study (0.5 mg/L) was similar to that in our study (2 mg/L).In a study by Wang et al., taniborbactam was reported to improve the activity of cefepime to the same level that avibactam improved the activity of ceftazidime against 66 KPC-2 producers and 30 non-carbapenemase-producing carbapenem-inter mediate/resistant Enterobacteriaceae (20).Vazquez-Ucha et al. reported cefepime-tani borbactam MIC 90 of 2 mg/L against a collection of 400 carbapenemase-producing Enterobacterales, noting that activity was excellent against OXA-48-and KPC-producing Enterobacterales but lower against MBL-producing isolates (21).Kloezen et al. found that cefepime-taniborbactam demonstrated potent activity against ESBL-producing Enterobacterales, restoring the susceptibility of all isolates tested (22).Karlowsky et al. tested the in vitro activity of cefepime-taniborbactam and comparators against a 2018-2020 collection of 13,731 Enterobacterales and 4,619 P. aeruginosa isolated from patients in 56 countries (23).This study showed that cefepime-taniborbactam exhibited potent in vitro activity against Enterobacterales and P. aeruginosa and inhibited most carbapenem-resistant isolates, including isolates carrying serine carbapenemases (KPC) or metallo-β-lactamases (NDM or VIM).Against Enterobacterales, MIC 90 was 0.25/4 mg/L, with 99.7% susceptible at a breakpoint of ≤16/4 mg/L.Against P. aeruginosa, MIC 90 was 8 mg/L, with 97.4% susceptible at a breakpoint of ≤16/4 mg/L.
A limitation of our study is that the isolates contained a limited spectrum of βlactamases other than KPC.Only seven isolates produced OXA-48-derived β-lactamases, with one of these coproducing a MBL (NDM-5).
In conclusion, cefepime-taniborbactam was active against most isolates in a set of carbapenem intermediate/resistant K. pneumoniae and P. aeruginosa isolates with carbapenem resistance mechanisms representative of those currently found in these species in the United States.Cefepime-taniborbactam was very active against KPC-pro ducing K. pneumoniae.
P. aeruginosa study isolates included 197 MDR clinical P. aeruginosa isolates collec ted as part of the Platforms for Rapid Identification of MDR-Gram-negative bacteria and Evaluation of Resistance Studies IV (PRIMERS-IV) study (11).These isolates came primarily from northeast Ohio and the mid-Atlantic states.Approximately half had been determined to be carbapenem-resistant when initially characterized.Isolates had been tested using two molecular diagnostic platforms, the Acuitas Resistome test (OpGen Inc., Gaithersburg, MD) and VERIGENE Gram-negative blood culture test (VERIGENE BC-GN, Luminex Corporation, Austin, TX), to identify genes that potentially confer resistance associated with porins, efflux pumps, and the presence of acquired carbapenemases (KPC and VIM).
MICs of cefepime-taniborbactam and comparators were determined using Sensititre custom frozen panels (ThermoFisher, Cleveland, OH) inoculated using cation-supplemen ted Mueller-Hinton broth (ThermoFisher).Taniborbactam was supplied by Venatorx Pharmaceuticals Inc. (Malvern, PA).In-house frozen panels were used to obtain cefepimetaniborbactam MIC endpoints of up to 128 mg/L for isolates with MICs of >8 mg/L from the initial panel.β-Lactamase inhibitors were tested at fixed concentrations in combination with varying concentrations of β-lactams, with avibactam, tazobactam, taniborbactam, and tazobactam tested at 4 mg/L and vaborbactam at 8 mg/L.Panels were inoculated according to standard methods and were read visually after incubation as previously described (9,10).MICs were interpreted using CLSI M100-S30 standard (12), with two exceptions.Meropenem-vaborbactam MICs for P. aeruginosa were not interpreted due to a lack of applicable breakpoints in the CLSI M100-S30 standard.Cefepime-taniborbactam MICs against both Enterobacterales and P. aeruginosa were interpreted using provisional breakpoints of ≤8 mg/L and ≤16 mg/L (susceptible) and >16 mg/L (resistant) (23), based upon in vivo efficacy data from neutropenic murine infection models (thigh, complicated urinary tract, lung) (13,14,17) and data from safety and pharmacokinetics studies in human volunteers (15,16).Quality control isolates E. coli ATCC 25922, E. coli ATCC 35218, K. pneumoniae ATCC 700603, K. pneumoniae ATCC BAA-1705, and P. aeruginosa ATCC 27853 were tested on each day of testing.
MIC values were analyzed and MIC distributions, categorical susceptibility, and MIC 50 and MIC 90 values were determined.Categorical susceptibility results were classified into two groups-susceptible and intermediate/resistant, the latter including intermediate, susceptible dose-dependent, and resistant interpretations.MIC values of β-lactam/β-lac tamase inhibitor combinations are shown as MICs of the β-lactam component.
The genetic basis of β-lactamase, porin ompK35 and ompK36, and ftsI (penicillin-bind ing protein 3, PBP3) genes in isolates of K. pneumoniae intermediate/resistant to one or more of the β-lactam/β-lactamase inhibitor agents tested or producing OXA-48-derived β-lactamases was determined by analysis of results of previously performed WGS (26) with reference genomes as follows.WGS analysis from the genome assembly and FASTQ files (NCBI BioProject PRJNA339843 for CRK0001-CRK0191 and PRJNA433394 for CRK0192-CRL0390) was performed using Geneious Prime version 2023.2 (Biomatters Inc., Boston, MA, USA).β-Lactamases in each genome were annotated using a search set of 90 representative β-lactamases with a cut-off of 40% identity and BLAST search at the Beta-Lactamase DataBase (BLDB) (http://www.bldb.eu/)(27).This search set identifies all ∼2,000 β-lactamases included in ResFinder 4.1 (28).The genes encoding major porins (ompK36 and ompK35) and the ftsI gene encoding PBP3 (the major target of cefepime) were analyzed using the gene sequences of a reference genome (Nucleotide accession NZ_KN046818.1).

a
MIC values of β-lactam/β-lactamase inhibitor combinations are shown as MICs of the β-lactam component.b No isolates with MIC indicated or concentration not tested.c MIC value greater than the previous MIC value.
the 197 tested MDR isolates of P. aeruginosa, 89 were carbapenem-susceptible and 108 were intermediate/resistant, with carbapenem resistance associated with porin changes or efflux pumps (n = 73), and with the presence of acquired carbapenema ses, KPC (n = 20) and VIM (n = 15).MIC distributions of cefepime-taniborbactam by carbapenem resistance mechanism are shown in Table 2 and Fig. 2. MIC 50/90 values and percentage of isolates susceptible to agents tested are shown in Table

TABLE 1
MIC 50/90 values and percent susceptibility of K. pneumoniae isolates (n = 200) a

Agent (susceptible breakpoint, mg/L) MIC range (mg/L) MIC 50 (mg/L) MIC 90 (mg/L) Percent susceptible
For comparative purposes only, the percent susceptible for cefepime-taniborbactam corresponds to the percentage of isolates inhibited at ≤8 and ≤16 mg/L. c

TABLE 2
Distribution of MICs of cefepime alone and in combination with taniborbactam for K. pneumoniae and P. aeruginosa isolates tested a

TABLE 4
MIC 50/90 values and percent susceptibility of P. aeruginosa isolates (n = 197) a a MIC values of β-lactam/β-lactamase inhibitor combinations are shown as MICs of the β-lactam component.b For comparative purposes only, the percent susceptible for cefepime-taniborbactam corresponds to the percentage of isolates inhibited at ≤8 and ≤16 mg/L.c No CLSI breakpoint is available.d Not applicable.

TABLE 5
MICs of β-lactam and β-lactam/β-lactamase inhibitor combinations of 18 P. aeruginosa isolates with KPC or VIM and susceptible to one or more of the β-lactam/β-lactamase inhibitor agents a,b

Agent (susceptible breakpoint, mg/L) MICs (mg/L) of 11 KPC-producing isolates MICs (mg/L) of 7 VIM-producing isolates Percent susceptible
a MIC values of β-lactam/β-lactamase inhibitor combinations are shown as MICs of the β-lactam component; shaded results indicate MICs in the susceptible range.b All other KPC-(n = 9) and VIM-producing isolates (n = 8) were intermediate/resistant to aztreonam and the β-lactam/β-lactamase inhibitor agents tested.c For comparative purposes only, the percent susceptible for cefepime-taniborbactam corresponds to the percentage of isolates inhibited at ≤8 and ≤16 mg/L.d No CLSI breakpoint is available.e Not applicable.